Processing devices can be utilized for a wide range of applications. For example, an electronic hearing aid includes a first processing device for converting electrical signals from a microphone into digital samples. A second processing device processes the digital samples to amplify or attenuate the particular frequencies where a user suffers hearing loss. A third processing device converts the processed digital samples into electrical signals used at a speaker for producing sound. In prior art systems, each of these processing devices is preprogrammed for their prescribed function. If the required function of the processing devices is to be modified from its original function, the processing devices must be sent back to the manufacturer for an adjustment.